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SWELTERING Brits should think again before wishing for heavy rain to dampen the current heatwave as it could have a devastating consequence.

A scientist has revealed how the extreme hot weather actually risks causing flash floods, if a massive downpour were to follow too soon.

Water is absorbed by land normally but it barely moves from a cup on dry landCredit: University of Reading

In an eye-opening video experiment Professor Rob Thompson, from the University of Reading’s meteorology department, demonstrates why it could be dangerous.

It comes down to how quick land is able to absorb rainfall.

Using a cup of water, the expert shows what happens to water on grass that's wet, grass during a normal British summer, and grass dried out by the heatwave.

Tipping the cup of water upside down on each patch, the dried out ground struggles to absorb any water at all, while the other two take it in a lot faster.

This means, if heavy rain were to drop suddenly with grass as scorched out as it is at the moment, we could be faced with serious flash floods.

"Britain desperately needs rain to break this drought," he told PA.

"But we should be careful what we wish for.

"Experience around the world has shown what can happen when heavy rain follows a very dry and hot period that has baked the soil hard.

"The water can’t soak in easily, most of it just runs straight off the surface, which can quickly turn into flash floods.

"If you’re praying for rain, you should pray for two days of drizzle, as dreadful as that sounds."

The Met Office has also warned about the very real threat it poses, saying: "This experiment shows how heavy rainfall following an extended period of extreme heat could lead to flooding."

Current forecasts suggest that isolated but intense thunderstorms are possible Sunday and Monday.

Some places could see about 50mm of rain falling in a three-hour period in the north.

Meanwhile, some areas further south may get around 30mm of rain in a three-hour period.

A drought has been declared for some areas of EnglandCredit: EPA

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